This invention relates to a spark plug boot keeper assembly and more particularly to a spark plug boot keeper assembly of a combustion engine utilizing a heat shield.
Spark plugs are known to have a male terminal protruding from an upper ceramic or terminal portion. A high voltage ignition wire terminal clip or female terminal is press fitted and thereby locks onto the male terminal of the spark plug. This high voltage electrical connection is surrounded by an elastomeric, electrically insulating boot which is integral to the ignition wire protruding from the top, and fits down snuggly around the upper ceramic portion of the spark plug. In addition to the boot""s insulating characteristics, the boot also assures that the high voltage electrical connection remains clean and free of moisture thereby providing a strong and efficient spark within the combustion chamber.
In today""s more complex combustion engines, the spark plug is often inserted into a deep spark plug well typically surrounded by an electrically grounded and heat dissipating engine block. After insertion into the well the spark plug is threadably engaged to the engine block. Because only the top of the spark plug is viewable when within the well, connection of the boot to the spark plug may be cumbersome. If the boot is not seated properly to the spark plug terminal, the strength of the resultant spark from the spark plug could be weakened, or the combustion process efficiency within a specific chamber might degrade thereby causing a rough running engine. Furthermore, repeated engagement and disengagement of the ignition wire to the spark plug during engine maintenance, or simply the vibration of a running engine itself, could weaken the female terminal clip causing the boot to disengage from the spark plug. Ensuring continuous and strong energy transmittal requires a commonly incorporated female terminal clip of a highly robust design. This robust or high strength design is expensive to manufacture and cumbersome to snap fit over the spark plug. Unfortunately, engineering a less expensive, weaker, female terminal could possibly cause the boot and terminal to unseat from the spark plug thereby producing a rough running engine and adding to warranty costs.
Furthermore, the spark plug and boot may be protected by a heat shield, also disposed within the well of the engine block, when heat dissipation from the engine block into the well is unusually high. The heat shield prevents the production of damaging hot spots on the elastomeric boot which could contribute to high voltage arcing from the ignition wire to the engine block, weakening the sparking characteristics of the spark plug. By surrounding the boot, the heat shield distributes and dissipates the otherwise damaging heat. Unfortunately, the heat shield must be installed into the well prior to threading the spark plug to the engine block. Therefore, the heat shield effectively narrows the spark plug well for purposes of seating the boot to the spark plug.
The present invention provides a spark plug boot keeper assembly which ensures that a spark plug boot is properly installed within a heat shield and locked onto a spark plug. The assembly has a spring clip which is pre-assembled to the heat shield via a locking extension protruding radially outward from the spring clip. The locking extension engages an axial inward facing surface of the heat shield. The locking extension preferably extends into a slot communicating through a wall of the heat shield and defined by the inward facing surface. The spring clip resiliently engages a bottom shelf of the heat shield which extends radially inward from the wall. A contact edge of the spring clip faces radially inward and engages or snap fits to a bottom portion of the spark plug after reeving over a radially protruding hexagonal portion of the spark plug during assembly.
A locking combination of the spark plug boot keeper assembly locks the boot to the spark plug by engaging the heat shield to an upward facing surface of the boot. An obstruction member of the locking combination extends radially inward from the wall of the heat shield disposed axially outward with respect to the outward facing surface of the boot. Preferably, a spring is compressed axially between the obstruction member and the outward facing surface of the boot thereby providing a constant axial inward force upon the boot. The heat shield and the pre-assembled spring clip can be withdrawn from the stationary spark plug upon a withdrawal force exerted on the heat shield causing the spring clip to expand radially outward.
A feature of the present invention is the ability to engage a heat shield to a spark plug pre-installed to the head of an engine block.
Another feature of the invention is providing a secondary means for securing the boot to the spark plug, other than the traditional ignition wire terminal clip snap fit engagement to the spark plug.
Yet another feature of the invention is reduced warranty costs by eliminating unintentional unseating of the boot from the spark plug and by providing a more robust electrical connection design.